1. Field of the Invention
The present invention relates to mine roof supports and, more particularly, to supports with goaf shields provided with the so-called lemniscate or figure-of-eight guide system.
2. Description of Prior Art
Known supports for use in underground mine workings employ one or more hydraulic props flexibly connected with ball-and-socket joints between roof and floor-engaging structures. The floor-engaging structure may be a single sill or a sub-divided sill with individual floor skids. The floor structure is linked via pivot joints to guide levers which connect with further pivot joints to a goaf shield pivotably suspended from the roof structure. The floor structure has bores providing journal bearings for pivot pins and one or more bearing sockets for the prop or props. If the effective height of operation of the support is insufficient for the mine working, it is known to insert an attachment which is fitted onto the floor structure to provide an alternative higher seating for the prop or props and an alternative higher linkage for the guide levers. The seating for the prop or props may also be adjustable in height with the aid of special lifting brackets equipped to fit in the socket or prop bearing in the floor structure and having a new socket at some distance above for re-locating the prop. (See German Patent Specification No. 3 519 904). This arrangement permits the use of props with a stroke smaller than the desired height adjustment of the support and the tendency of longer props to buckle is thence precluded. The use of known forms of attachment nevertheless gives rise to problems since the attachment is invariably linked to the floor structure with just two connecting bolts or pins. Since the forces exerted on the goaf shield have to be transferred to the floor structure excessive stresses can occur on the connectors giving rise to failure.
A general object of the invention is to provide an improved support of the aforementioned kind and particularly a support which will enable high forces to be reliably transferred to the floor structure at all times.